Vacuum Pumped Liquid Cooling System for Computers

ABSTRACT

A reliable, leak tolerant liquid cooling system with a backup air-cooling system for computers is provided. The system may use a vacuum pump and a liquid pump in combination to provide negative fluid pressure so that liquid does not leak out of the system near electrical components. The system distributes flow and pressure with a series of pressure regulating valves so that an array of computers can be serviced by a single cooling system. The system provides both air and liquid cooling so that if the liquid cooling system does not provide adequate cooling, the air cooling system will be automatically activated. A connector system is provided to automatically evacuate the liquid from the heat exchangers before they are disconnected.

BACKGROUND OF THE DISCLOSURE Brief Description of the Related Art

Arrays of electronic computers, such as are found in data centers,generate a great deal of heat. A typical CPU puts out over 100 watts andhas a maximum case temperature of about 60 C. A typical rack of 88 CPUsmay put out 9 Kw. The maximum outside temperature at a hot urbanlocation might be 45 C, so the heat flow goes with the gradient.Theoretically, no refrigeration should be required, yet the standard wayto keep data centers cool is to use vapor compression refrigerationsystems at least part of the time. These systems often use more powerthat the computers themselves. These systems use air as the heattransfer medium, and it is due to the low heat capacity and thermalconductivity of air that refrigeration must be used to overcome thethermal resistance of multiple air heat exchangers. Some operators useevaporation of water to cool water-to-air heat exchangers which then inturn cool computers, and this is more efficient than refrigeration, butthe computers run hotter, thus reducing their reliability and making thedata center uncomfortable. Water has 4000 times more heat capacity thatair of the same volume, so water is an ideal heat transfer agent fordirect heat transfer from the heat generating components. However,operators of server systems are concerned about leaks and reliability ofwater-cooled computers. One potential issue with water-cooled negativepressure systems is that at low absolute pressures, water may boil. Forexample, at 50 C, water boils at 4 in Hg, so the system pressure cannotget that low. Therefore, a pump must be used with low NPSH, so that thewater does not cavitate at the pump inlet. One such pump is described bythe inventor in U.S. Pat. No. 7,611,333, the disclosure of which isincorporated herein by reference. What is needed is a cooling solutionadaptable for up to a large number of computers, that uses a minimumamount of water flow, is reliable, leak-free and low in powerconsumption.

Therefore it is an object of the present invention to provide a reliablecooling system to a large number of CPUs under negative pressure, with aminimal chance of leakage, and with an air cooling backup system. It isalso an object of the present invention to provide a cooling solutionwhich integrates with an air cooled heat sink for backup and utilizesonly the minimum amount of water to provide adequate cooling for eachheat generating element. Furthermore, it is an object of the presentinvention to provide a device to disconnect and reconnect serverswithout losing any water.

SUMMARY OF THE DISCLOSURE

A system provides water cooling under negative pressure for an array ofcomputers or other heat generating devices with a minimal flow rate anda minimal volume of water in order to provide cooling in an efficientand reliable manner. In certain embodiments the system includes anoutdoor cooling tower to cool water, a water distribution system tosupply water to multiple CPUs, high performance heat exchangers toremove heat from said CPUs with a minimum flow rate and delta pressure,a water pump to suck water through said CPUs and a vacuum pump to removeany air which may enter the system. In addition the system may includean air-cooled heat exchanger attached to each CPU to remove the heat inthe event that the liquid cooling system is not operating.

The system may use a cooling tower to cool down the water usingconvection and evaporation in order to reduce the temperature to thelocal wet bulb temperature or whatever temperature is required by theCPUs, which is typically less than 30 C. The cool water is preferablyprovided under a pressure which is less than the local atmosphericpressure to a rack and then to a server with one or more heat generatingcomponents, such as CPUs. The entire system preferably runs at a lowabsolute pressure, so that any leaks are of air into the system, ratherthan water out of the system. This limits the available delta pressureavailable to each heat exchanger to the difference between the vaporpressure of the warmest water within the system and the local absolutepressures. Therefore, delta pressures are allocated to each heatexchanger that are substantially less than 1 atmosphere. Thewater-cooled heat exchanger is preferably mounted to the CPU andcomprises a passage with a turbulator to increase the velocity andturbulence of the water near the heat transfer surface. The turbulatormay also be designed to minimize the volume of water contained withinthe server so that the water may be quickly cleared for repairs. The CPUtypically includes an air-cooled heat exchanger with fins and a fanlocated nearby to provide air-cooling. The fan may be controlled by thetemperature of the CPU so that as it gets hotter, the fan increases inspeed. The liquid flow rate may be determined by the acceptabletemperature rise of the liquid and the power dissipated by the CPU. Fora typical CPU that puts out 100 watts, a stream of water at 150cc/minute will result in a temperature rise of approximately 10 C. Thetemperature differential from the CPU case to the water should be of thesame order as the temperature rise. The heat exchanger should have apressure drop of approximately 4 in Hg so that the system will workproperly on a hot day in a high altitude location, where the differencebetween the local atmospheric pressure and the vapor pressure of the hotwater can be only 8 inches Hg.

The fan which is connected to the CPU heat exchanger may also be used tocool the interior of the computer by transferring heat from the airinside the computer to the water so that other components within theserver enclosure may be cooled with or without the use of external airflow.

The water reservoir is preferably at lower pressure than the devicesbeing cooled. This can be accomplished by keeping the reservoir at alower elevation than the CPU or by means of a check valve with a givencracking pressure or a pressure regulator. This will provide negativepressure at the CPU by means of gravity head. The water distributionsystem provides the water at a pressure of approximately −2 in Hg to theservers. This may be accomplished by means of the system design, or byplacing a pressure-regulating valve at the server or rack level. Theplumbing from the fluid supply reservoir to the server may require apump if the server is at a significantly higher elevation than thecooling tower, such as if it is on a different floor than the coolingtower. The supply pump speed may be controlled so that the pressure atthe server is at the correct value.

The plumbing to and from the server may be designed for low pressuredrop, so as to keep the total system delta pressure within limits.Alternatively, the plumbing to the server racks may be high pressureplumbing supplied by a pump, with a pressure regulator to reduce thepressure to below atmospheric as the water gets close to theelectronics. For the return system, larger pipes may be required for theflow of air and water, as air will be introduced to the system asservers are removed or replaced. Local air removal systems may be usedin order to prevent the return plumbing from getting too large. Suchsystems may use local vacuum pumps, plumbing to a central vacuum pump,or float actuated valves and multiple compartments, as in U.S. Pat. No.4,967,832, which is incorporated herein by reference in its entirety.

Server Pressure Regulators

Each server may have an inlet pressure regulator and an outlet pressureregulator in order to maintain a desired delta pressure across the CPUheat exchanger. Each CPU will typically have a temperature sensor, andan increase in temperature over the inlet water temperature may indicatea problem with the heat exchanger. This may be used to indicate a needfor repair. A temperature sensor, such as a thermistor, may be used tomeasure the inlet water temperature. Flowmeters, such as a rotameter orturbine meter with a digital readout, may also be used to monitor theflow. A filter may be used after the cooling tower and before the heatexchanger to prevent clogging of the heat exchanger passages. Chemicaladditives may be used to prevent fouling of the heat exchanger withbiological films and to prevent corrosion. The internal heat exchangerpassages may be plated or anodized to prevent corrosion.

Local Air Release

A vacuum reservoir may be located at each server rack, and it may have afloat actuated air release to allow for the release of any accumulationof air. Such local air release systems may require local vacuum pumps orconnection to a central vacuum system.

Interconnect with Draining Provision

Each server or server rack may be connected with a dry disconnect systemthat allows for the automatic draining of the server system. Thisconnector may include the supply and return flows. Such flows may becoaxial, in order to allow for a small interconnect. The system ispreferably designed to remove all of the water from inside eachsubsystem such as a CPU, server or server rack during the disconnectionprocess. For example, if the server contains 1 cc of water, and the flowrate is 150 cc/minute of water, then it will take less than 1 second todrain the water out of the system. As the water is replaced by air, theflow resistance of the heat exchanger decreases, so the process mayhappen in less than 0.5 seconds. This draining process is helped by thefollowing connector arrangement. To detach the connector in oneembodiment discussed below, the operator would depress a button thatoperates a three-way valve that cuts off inlet water flow and vents toallow air into the system. Negative pressure on the return side of theconnector holds the connector in until air reaches the outlet. At thispoint, the negative pressure in the system is diminished due to the muchlower delta pressure of air flowing through the heat exchanger and thenthe connector may be easily removed. Removal of the connector seals theoutlet so that air does not continue to flow into the cooling systemreturn flow path. The button stays depressed, thereby sealing off theinlet. To attach the connector, the operator would insert the coupling,which would connect the return path, and the button would automaticallyrelease, which would allow the supply flow to reach the components. Thissystem may also be actuated with a twist instead of a button push. Theconnector may utilize a sacrificial metal, such as zinc or utilizeelectrical potential to prevent corrosion inside the CPU heat exchanger.

The fluid and vacuum pumps for the system are preferably reliable andhave a long life. They should also provide a steady pressure on thesuction side, and a low pressure on the outlet, in order to deliver flowto the cooling tower. One preferred design for maximum operational lifewould be to use a dual chamber pump such as described in, for instance,U.S. Pat. No. 7,611,333, which is incorporated herein by reference, dueto the very low net positive suction head required and due to itsability to reject bubbles from the inlet flow. Such a pump, when drivenby a vacuum pump and an air compressor, could provide a very low inletpressure and an independent output pressure. This type of pump could befitted with additional backup vacuum pumps and compressors connectedwith check valves so that any single point failure would not cause asystem-wide failure. In addition, the check valves and pressurizationand vacuum valves and controls could include redundant units.

An alternative would be to use a fluid pump and a vacuum pump. For thefluid pump, a seal-less centrifugal pump with a magnetic drive wouldwork well, as would a solenoid pump with an internal fluidic checkvalve, such as is described by Tesla in U.S. Pat. No. 1,329,559, whichis incorporated herein by reference. In these cases, a fluid pump couldbe placed in parallel with a vacuum pump, with both connected to areservoir. The vacuum pump could be a piston type with a Teflon orsimilar seal, which has a long lifetime, or it could be a linear pump ora diaphragm pump. The pump must be compatible with the humidity and anychemical used to prevent corrosion or biofilm growth. A float valve, asis well known in the art, may be used to keep water out of the inlet ofthe vacuum pump.

In one embodiment, the system contains a reservoir of cool water, whichsupplies water to a heat exchanger, with the heated water returned toone or more reservoirs maintained partly full of water, the water levelbeing maintained by a vacuum pump and a water pump.

The vacuum reservoir may include a regulator to maintain constantpressure and a level switch, such that if the liquid level is too high,the liquid pump speed is increased, sucking liquid out of reservoir andpumping it into a cooling tower. This provides a constant pressuredifferential to multiple heat sources.

For a system that uses a liquid pump, it may be necessary to prime thesystem. This may be accomplished by turning the liquid pump off andallowing fluid to flow backwards through the pump. A flow actuatedshuttle valve in the pump output may be at a default off positionallowing the vacuum pump to suck fluid into the reservoir. Once theliquid pump is primed and the level sensor activated, the liquid pumpmay then turn on and pump the fluid out of the reservoir and into thecooling tower.

The heat exchanger may use a helical flow pattern to put a long pathinto a short passage. This may be accomplished by placing a threaded rodin a metal tube so that the flow must take a long path through the heatexchanger at a high velocity. This has the added benefit of reducing thevolume of water in the heat exchanger, thereby reducing the amount ofwater that needs to be cleared to service the heat exchanger.Alternatively, a rod with a tortuous path in relief may be used toincrease the water flow and turbulence. The rod and cylinder may besquare or of any other cylindrical shape. The turbulator may be designedso that some of the water flows over the flow passages in an axialdirection. This axial flow will interact with the helical flow toprovide swirl in the heat transfer passages in order to increase heattransfer. In addition, the axial flow will reduce the flow resistance ofthe heat exchanger. This arrangement may be particularly useful insituations where the flow is laminar. For high power dissipationsystems, multiple parallel turbulators may be used. In someinstallations, a flat plate heat exchanger may be used.

Although a CPU is described, this system maybe used to cool anyelectronic component. Although water is described, any coolant may beused instead of or in addition to water. Although the system isdescribed as using water for evaporation and for cooling, a liquid toliquid heat exchanger may be used to transfer heat from an evaporativesystem to a closed system so that a non-corrosive or non-conductivecoolant may be used for the CPUs. This may be used in the case ofevaporative coolers which use salt water or reclaimed water, forexample. For low temperature operation, as in Northern latitudes, aradiator, fan and glycol system may be used to reject the heat andprevent freezing of the coolant. Since CPUs can get up to 60 C, watercan be heated to 50 C and used for hot water service. The water used forcooling the computers may be kept at a temperature higher than the dewpoint of the air in the data center to prevent condensation on theplumbing or the heat exchangers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a vacuum-pumped liquid cooling system accordingto one embodiment

FIG. 2 is a top view of a typical air and water-cooled heat exchangerwith turbulator.

FIG. 3 is a section view of a typical air and water cooled heatexchanger with turbulator.

FIG. 4 is an isometric view of a typical turbulator.

FIG. 5 is a diagram showing an example water clearing disconnect systemunder normal operation.

FIG. 6 is a diagram showing an example water clearing disconnect systemduring the disconnect process.

FIG. 7 is a diagram showing an example water clearing disconnect systemin a disconnected state.

FIG. 8 is a diagram of an alternate embodiment of a vacuum-pumped liquidcooling system.

FIG. 9 a is a section view of a vacuum accumulator used to prevent dropsof water from leaving the system when it is disconnected, shown in alow-vacuum condition.

FIG. 9 b is a section view of the vacuum accumulator of FIG. 9 a, shownin a high-vacuum condition.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The following detailed description presents a description of certainexample embodiments of the present invention. In this description,reference is made to the drawings wherein like parts are designated withlike numerals throughout.

Referring to the example embodiment shown in FIG. 1, a supply of liquidcoolant such as water 12 is maintained at a low temperature by theevaporation of the water as it flows out of nozzle 13. The humid airflows out due to fan 14 in cooling tower 11. Due to the low pressure inthe reservoir 6, the water flows through a filter 9, and check valve 18and a supply pipe 5, through a pressure regulator 3, through anothercheck valve with a cracking pressure of approximately 1 inch HG, throughand vacuum accumulator 17 and then through a fluid connector 2, to thecomputer with internal heat exchanger 1. The water then receives heatfrom the internal electronic components in the computer and flows outthrough the connector to an extraction pipe 4 and then to the reservoir6. A vacuum is maintained within the reservoir by the vacuum pump 8. Thevacuum pump 8 may be controlled by the pressure sensor 15 to maintain anabsolute pressure which is above the vapor pressure of the water in itsheated state. The reservoir 6 may include a level sensor 7 such that ifa certain level is exceeded, the liquid pump 10 speeds up, therebypumping liquid out of the reservoir 6 and into the cooling tower 11. Thecooling tower 11 will require makeup water to replace water that isevaporated, as is known in the art of evaporative coolers generally. Inaddition, a system may be required to prime the pump 10, as is known inthe art of pumps.

Referring to FIG. 2, an example air and water heat exchanger 200comprises a water cooling portion 210, which includes inlet tube 22 andoutlet tube 23 to provide water (not shown) to the turbulator 20 (shownin more detail in FIG. 4), and a metal heat spreader 24 that is inthermal contact with the electronic device (not shown) on one side andthe water on the other. A series of fins 21 are provided in thermalcontact with flowing air in the event that the liquid cooling system isnot operational. A fan (not shown) would typically be used in proximityto the fins 21 to provide cooling air. A turbulator 20 fits inside themetal heat spreader 24 and reduces the amount of water needed to coolthe device and increases the velocity and turbulence level in the water.In this device 200, the water inlet 22 may be adapted to provide a pointof jet impingement cooling closest to the heat source, and to flow thewater in a helical path through the turbulator 20 to the outlet tube 23.In some cases a portion of the flow may flow over the helical flowpassages in the turbulator 20 in short circuit from the inlet 22 to theoutlet 23. This flow may enhance heat transfer by causing the helicalflow to swirl.

FIG. 3 shows a partial cross-sectional side view of the air and waterheat exchanger 200 shown from the top in FIG. 2. The turbulator 20 canbe seen installed in the heat spreader 24, and providing a narrowhelical path 25 for the cooling water. The CPU is not shown in thisview; it would normally be attached to the bottom or lower portion ofthe heat spreader 24. FIG. 4 provides an isometric view of theturbulator 20, which shows the helical flow path 25 more clearly.

FIG. 5 provides a diagram of an example water clearing system in normaloperation, depicting the water flowing through a supply valve 71 and,and then through a heat exchanger, 21, and then out through a returnvalve 72. In this configuration the valves 71, 72 are sealed from theoutside air.

FIG. 6 shows a diagram of the water clearing system of FIG. 5 during thedisconnect process. Before disconnecting the fluid supply and extractionlines (not shown), the user activates valve 71 which allows air to flowinto the heat exchanger 21, shown schematically. The valve 71 may beconnected to a latch (not shown) that prevents the fluid lines frombeing removed until the valve is depressed. The latch can be configuredto remain in a latched position, so valve 71 remains activated until theconnector (not shown) is reinserted into the computer.

FIG. 7 shows a diagram of the water clearing system of FIG. 5 uponcompletion of the disconnect process, such that the heat exchanger 21 isdisconnected from the liquid cooling system. In this case, the supplyvalve 71 remains activated so that air does not flow into the coolingsystem. And return valve 72 is also activated so that air does not flowinto the cooling system. Return valve 72 may be activated by a pin orlatch (not shown) so that it shuts off when the heat exchanger 21 isdisconnected from the liquid cooling system. The connector may bedesigned to be retained until all the liquid is removed from the heatexchanger. This retaining feature would be activated by thesubatmospheric pressure due to the suction in the return line. However,once the heat exchanger was no longer full of water, there would be lessdelta pressure across the heat exchanger.

Referring now to the example embodiment shown in FIG. 8, the centrifugalpump 8 and reservoir 6 of FIG. 1 has been replaced by a multiple chamberpump which acts as a vacuum pump, reservoir, water/air separator andpressure pump. In this embodiment, the system may use two reservoirs, amain reservoir 6, and an auxiliary reservoir 56. The operation of thissystem is as follows: the water flows in to the reservoir 6 from theextraction pipe 4 through the check valve 49 under suction. The pressurein the reservoir 6 is maintained at a low level by vacuum pump 8, whichis connected to the reservoir by open valve 44. A vacuum reservoir, 55may be used to provide a steadier suction. The water flows into thereservoir 6 until the level sensor 41 indicates that the reservoir 6 isnearly full. Then the valve 34 opens, lowering the pressure of auxiliaryreservoir 56 so that water may flow into it as well through check valve38. Once flow is established into both reservoirs 6, 56, valve 44 shutsand valve 43 opens, thereby pressurizing main reservoir 6 so that waterflows through check valve 48 and into the cooling tower 11. Then thelevel in reservoir 6 reaches a low level, as indicated from level senor42, at which time the valve 43 shuts. Then the valve 44 opens and flowis established under suction into the main reservoir again, at whichtime the auxiliary reservoir vacuum valve, 34 is shut and thepressurization valve 33 is opened forcing water out through check valve39 until the level in the reservoir reaches the low level sensor 32. Thelevel sensor 31 can be used to indicate if there is a system failure,under normal operation it would not be needed because the system isdesigned so that the flow out of the reservoirs 6, 56 is higher than theflow into the reservoirs 6, 56, so the auxiliary reservoir 56 is nevercompletely full, thereby allowing for the flow through the heatexchangers 1 to be steady while the flow to the cooling tower 11 isintermittent. The pressure and vacuum levels can be monitored by thepressure pump 53 and the vacuum pump 8 using the pressure sensors 54 and15. The entire system can be controlled by a computer or by a logiccircuit. A float 51 may be used to sense the level and reduceevaporation of the water in the reservoirs.

Referring to FIGS. 9 a and 9 b, a vacuum accumulator 17 is shown, havinga liquid inlet 61 and liquid outlet 63. The vacuum accumulator 17comprises a flexible diaphragm 62 which may be flat or nearly flat whenno pressure differential exists between inside and outside theaccumulator 17, as in FIG. 9 a. When a vacuum or pressure less than theexternal atmosphere is provided by the system inside accumulator 17, thediaphragm 62 is displaced into the liquid and holds a steady position asshown in FIG. 9 b. If the CPU is disconnected from the rest of thesystem, then the check valve 16 shuts and the diaphragm 62 springs backinto the flat position as in FIG. 9 a. This tends to prevent dripping ofliquid out of the system.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodification, and this application is intended to cover any variations,uses, or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent invention as would be understood to those in the art asequivalent and the scope and context of the present invention is to beinterpreted as including such equivalents and construed in accordancewith the claims appended hereto.

1. A system for cooling an electrical device, comprising: afluid-containing heat exchanger thermally coupled to the electricaldevice; a fluid-containing reservoir in fluid communication with theheat exchanger, the reservoir defining an opening, the reservoirpartially full of coolant fluid such that the coolant fluid is at alevel below the opening; a fluid pump in fluid communication with thereservoir and the heat exchanger; and a vacuum pump in vacuumcommunication with said opening in said reservoir; wherein the fluidpump in combination with the vacuum pump causes the coolant fluid toflow from the reservoir through the heat exchanger and back to thereservoir under less than atmospheric pressure.
 2. The system of claim1, further comprising: a second heat exchanger thermally coupled to theelectrical device, the second heat exchanger adapted to transfer heatfrom the electrical device to the air surrounding the second heatexchanger; and a fan adapted to move air past the fluid-containing heatexchanger.
 3. The system of claim 1, wherein the fluid-containing heatexchanger is adapted to transfer heat from the electrical device to theair surrounding the fluid-containing heat exchanger, further comprisinga fan adapted to move air past the fluid-containing heat exchanger. 4.The system of claim 1, further comprising: an evaporative cooling towerin fluid communication with and thermally coupled to the coolant fluid.5. The system of claim 1, wherein the fluid-containing heat exchangerfurther comprises a turbulator adapted to cause the coolant fluid toflow in a helical path.
 6. The system of claim 1, wherein the coolantfluid flows over a plated surface.
 7. The system of claim 1, furthercomprising: a fluid level sensor located in the reservoir and providingan output based on the level of the fluid in the reservoir, the fluidpump being adapted to operate in response to the output of the fluidlevel sensor.
 8. The system of claim 1, further comprising: a fluidlevel sensor located in the reservoir and providing an output based onthe level of the fluid in the reservoir, the fluid pump being adapted tooperate in response to the output of the fluid level sensor and tomaintain the fluid level in the reservoir within a range.
 9. The systemof claim 1, further comprising: a vacuum regulator in vacuumcommunication with the vacuum pump and adapted to maintain a pressure inthe reservoir less than atmospheric pressure.
 10. The system of claim 1,further comprising: a fluid filter in fluid communication with thefluid-containing heat exchanger and adapted to prevent debris fromentering the fluid-containing heat exchanger.
 11. The system of claim 1,further comprising: a coolant fluid pressure regulator in fluidcommunication with the fluid-containing heat exchanger, the coolantfluid pressure regulator adapted to provide a constant pressuredifferential across the fluid-containing heat exchanger.
 12. The systemof claim 1, further comprising: a vacuum accumulator in fluidcommunication with the fluid-containing heat exchanger.
 13. The systemof claim 1, further comprising: a connector releasably connecting thefluid-containing heat exchanger to the fluid-containing reservoir, theconnector adapted to release the fluid-containing heat exchanger fromthe fluid-containing reservoir only when substantially all of thecoolant fluid has been evacuated out of the fluid-containing heatexchanger.
 14. The system of claim 1, further comprising a plurality offluid-containing heat exchangers thermally coupled to a plurality ofelectrical devices.
 15. The system of claim 1, further comprising an aircompressor in fluid communication with at least one reservoir, saidcompressor configured to pump said coolant fluid out of said reservoir.